1. Field of the Invention
The present invention relates to an auxiliary rotation-system starter which is used in starting an engine of an automobile for example.
2. Description of the Related Art
FIG. 8 is an electrical connection diagram showing a configuration of a conventional auxiliary rotation-type starter disclosed in Japanese Utility Model Laid-open No. Sho 57-174760. Referring now to FIG. 8, in a conventional auxiliary rotation-system starter 101, a starter motor 102 is electrically connected to a battery power source 105 through a main circuit portion 103 and an auxiliary circuit portion 104 connected in parallel with the main circuit portion 103. The main circuit portion 103 has a main contact portion 106 for enabling or disabling the electrical connection between the battery power source 105 and the starter motor 102. The auxiliary circuit portion 104 has a driving coil portion 107 for opening or closing the main contact portion 106. The auxiliary circuit portion 104 is provided with a relay 108 for enabling or disabling the electrical connection between the battery power source 105 and the driving coil portion 107. In addition, the main circuit portion 103 is provided with a fuse 109. The fuse 109 is disposed between the main contact portion 106 and the starter motor 102.
A pinion gear 110 which serves to be moved axially along with the opening or closing of the main contact portion 106 is coupled to the starter motor 102. In addition, a ring gear 111 which is coupled to an engine is disposed in the vicinity of the pinion gear 110. The pinion gear 110 is engaged with the ring gear 111 due to the movement thereof resulting from the closing of the main contact portion 106.
Next, the operation of the auxiliary rotation-system starter 101 will hereinbelow be described. First of all, closing the relay 108 energizes and activates the driving coil portion 107 and the starter motor 102, respectively. At this time, since the starter motor 102 is activated through the driving coil portion 107, a relatively small torque is supplied to an output shaft of the starter motor 102 to put it into a state of auxiliary rotation. In addition, since the driving coil portion 107 is energized, closing of the main contact portion 106 starts along with the pinion gear 110 being moved towards the side of the ring gear 111. As a result, the pinion gear 110 is moved as it is being auxiliarly rotated.
The pinion gear 110 is brought into contact with the surface of the ring gear 111 due to this movement. At this time, since this operation entails the auxiliary rotation, the pinion gear 110 is slid while being pressed against the surface of the ring gear 111. At this time, when the teeth of the pinion gear 110 have reached the insertion position between the teeth of the ring gear 111 due to the sliding, the teeth of the pinion gear 110 are inserted between the teeth of the ring gear 111 so that the pinion gear 110 is engaged with the ring gear 111. In addition, concurrently with the engagement, the main contact portion 106 is closed. Closing the main contact portion 106 causes a current to flow through the main circuit portion 103 to rotate the starter motor 102 at high speed, thereby cranking the engine.
Although in such an auxiliary rotation-system starter 101, there is a fear that the temperature of the main circuit portion 103 and the auxiliary circuit portion 104 can become extremely high due to, for example long current flow during cranking, the overruns or the like, the fuse 109 provided in the main circuit portion 103 will fuse, thereby preventing this extremely high temperature state from occurring.
However, since the value of the current made to flow through the starter motor 102 during the cranking is larger than that of the current made to flow through the starter motor 102 during the auxiliary rotation, the melting capacity of the fuse 109 provided in the main circuit portion 103 is set with the value of the current made to flow therethrough during cranking as the reference. With such capacity setting for the fuse 109, however, no current during the auxiliary rotation is cut off. For this reason, in the case where the pinion gear 110 is not perfectly engaged with the ring gear 111 due, for example, to catching on an alien substances, scratches or the like for example so that the auxiliary rotation of the starter motor is continuously carried out, there is encountered the problem that the current is made to flow continuously through the driving coil portion 107 for a long time, causing the coil thin film to fuse.